a. Field of the Invention
The present invention relates generally to passing voice communications over a data communications network such as an asynchronous communications network or a synchronous communications network.
b. Background Information
Almost all customers of data traffic today have additional, separate links to carry voice. This is inefficient for the customer and the communications provider. Many are seeking techniques that place Ds0 channels in data packets for transmission over a data link, so that they can remove their voice links.
A communications network serves to transport information among a number of locations. The information is usually presented to the network in the form of time-domain electrical signals and can represent any combination of voice, video, or computer data. A typical communications network consists of various physical sites called xe2x80x9cnodes,xe2x80x9d interconnected by conduits called xe2x80x9clinks.xe2x80x9d Each link carries information from one site to another site. End user sites may contain data terminating equipment (DTE) for combining, separating, and transforming data with or without voice. Network provider sites usually include either edge switches, with user network interfaces (UNI), or backbone switches, which only connect to other backbone switches and edge switches and do not contain UNI.
Voice information is carried via a Ds0 (or voice) channel that is a 64 kilobits per second (64 Kbps) channel and also the worldwide standard for digitizing voice conversation. The channel throughput is 64 Kbps because a digital data stream can adequately represent an analog voice signal if sampled at a rate of 8000 samples per second. If each voice sample is digitized using 8 bits, this results in a digital data stream of 64 Kbps. Since Ds0 is a synchronous TDM link, once a channel connection has been setup between two users, that channel is dedicated until the connection is torn (or brought) down, and cannot be used by anything or anybody else even if there is silence in the line.
Data currently is transmitted between nodes either as synchronous or asynchronous. In a synchronous network using Synchronous Transfer Mode (STM), each timeslot is assigned a certain time when it is to arrive at each node. The time when the timeslot arrives determines where the timeslot goes. Thus, the individual timeslots do not need to have routing information within them.
Asynchronous Transfer Mode (ATM), Frame Relay (FR), and Internet Protocol (IP), collectively called data, are considered asynchronous because each node in the network does not know until after a data packet arrives where it is intended to go. The arrival of a particular data packet at a node, on the other hand, is not guaranteed to occur at a particular point in time. Only by analyzing the routing information in the header can the data switch know where to route the data packet.
Asynchronous Transfer Mode is designed to be carried over the emerging fiber optical network, called the Synchronous Optical NETwork (SONET), although it can be carried over almost any communications link. The basic unit of ATM is a data packet called the ATM cell. Each cell contains two parts, a header, which contains routing information, and a payload, which contains the data to be transported from one end node to another. The ATM cell is always the same size.
Frame Relay and Internet Protocol are two other asynchronous types of communications protocols. Each is similar to ATM in that they also consist of a data packet. However, they differ from ATM in that their packet size can vary from packet to packet, and both can be considerably larger than ATM. This allows them to make more efficient use of the bandwidth of the communications media they travel over, but it makes receiving them more difficult in that packet size must be calculated for each packet. Both the FR protocol and IP may be used in point to point connections, but IP may also be used when multiple ports are connected to a single transmission medium.
Data can consume as much or as little as is needed for carrying actual traffic, because data does not reserve a fixed amount of bandwidth per link. While voice will never overload, or oversubscribe, the capacity of its links, there are mechanisms in place to handle data overloads when more is available than a physical link can carry. It is these mechanisms that allow data network designers to specify more data demand than capacity to carry, which is a process called statistical multiplexing.
Statistical multiplexing is the concept of giving multiple customers, in sum total, more bandwidth through a physical connection than it can carry. This is also known as over-subscribing. Studies have shown that customers will not always use all of the bandwidth their carrier has set aside for them. It is during this period of non-use by a customer that spare bandwidth is available for the over-subscription. If sufficient numbers of customers are placed on a single physical connection then large quantities of spare bandwidth can be realized.
When traffic is isolated among two or more physical connections, less statistical multiplexing can occur, as customers on one connection cannot use spare bandwidth on another. By joining all customers into a single, large connection, better statistical multiplexing occurs and the carrier is able to sell more bandwidth on one high-speed physical connection than on several smaller connections whose sum is equal to the one high-speed connection.
There are different ways of handling overloads in the data network. In ATM, the network is designed with large buffers which absorb the excess traffic, queueing it up until capacity is available to place the traffic through the network. The traffic that is delivered out of its buffers first is determined by the quality of service (QOS) the customer has paid the carrier to provide. Higher QOS traffic is removed from its buffers before lower QOS. This is important for real time applications such as voice or interactive TV services, which must get through the network with a minimum amount of delay.
In those instances where so much excess traffic is delivered that the network cannot queue it up in buffers, the lower QOS traffic is deleted, or dropped, from the buffers to make room for higher QOS traffic to be queued up. Ideally, customer end-to-end protocols will detect this loss of traffic and will re-transmit the lost information.
An emerging standard in the IP network uses a different approach to handling overloads. In IP, there is no QOS as in ATM. Once a data packet is injected into the IP network, it will be given equal priority with all other traffic and delivered to its destination with a minimum of delay.
In an IP network, the traffic density in a link is closely monitored. As it begins to approach the link capacity, the IP data switch send congestion notices back towards the data sources telling them to slow down the amount of data they send. Each notice will, for a limited length of time, force the data source to restrict what it sends out. As link traffic gets closer and closer to link capacity, more of these messages are sent backwards. When an IP switch receives congestion notices and reduces the rate of transmission, it may experience congestion as well and will send congestion notices back to its sources.
Eventually, the notices reach the traffic origins, customers. The customer equipment must then cut back on what is sent into the network, and must decide which traffic it puts out has the highest priority so that it goes out while the lower priority traffic has to wait. Thus, the IP network passes the job of determining traffic priority to the customer. If a customer has a great deal of high priority traffic, it may pay a premium to not receive as many congestion notices when congestion hits the network as another customer may pay, so that it will get more guaranteed traffic during congestion.
The IP data switches also usually maintain small buffers, but these are designed exclusively to handle the small, temporary overloads that occur until the congestion notices are responded to and reduced traffic flows into the switch.
These two different means of determining traffic priority are given as an example only. Whatever the mechanism, voice will usually be given a higher priority than data. By ensuring that the voice traffic does not physically exceed the capacity of the network links, the network systems engineering team can ensure all voice gets through, squeezing out the needs of data traffic. This allows the physical links to stay at or close to capacity even as the demands of Ds0 change. This spreads the cost of the links out over more traffic, reducing the cost per data packet and thus making the network more efficient than dedicated links carrying voice can be.
Each of ATM, FR, and IP has certain benefits and certain disadvantages. By utilizing these protocols in areas where their benefits can be utilized to the maximum efficiency while minimizing the losses incurred from their disadvantages, a more efficient network is realized.
Because of its fixed size packet, ATM is more attractive on the higher speed links where it is considerably less expensive to design hardware to receive a fixed size packet than a variable sized packet. On the lower speed, but higher per-bit cost links, FR and IP are more attractive because of their line utilization efficiency. And at these speeds the cost difference between a port that can receive variable sized packets versus one that only has to receive fixed size packets is usually more than offset by the fact that there are no segmentation and reassembly functions that have to be performed. Segmentation and reassembly is needed when a variable sized message is placed in multiple data packets, which is necessary with ATM.
Improvements in the state of the art of design technology are making the segmentation and reassembly functions less expensive. On the other hands, similar improvements are making it easier to design IP and FR receivers that can operate at SONET rates. What will likely happen is that the industry will see ATM, which is maturer than IP, dominate the high-speed market for the next 5 to 10 years. After that time period, IP, which has a simpler and less expensive congestion management scheme than ATM, will become the dominant mechanism in high-speed traffic.
On a bit per bit basis, it is significantly less expensive to transmit data over fiber than using metallic links by several factors of ten. The theoretical capacity of fiber is in excess of 20 tera bits per second (20 million million bits per second). Current standards at 10 thousand million bits per second (gigabits per second, or gbps), and will soon increase to 40 thousand million bits per second. Furthermore, technology is also improving on the ability of a single fiber to carry numerous wavelengths, or colors. Each wavelength can carry 10 gbps independently of what the other wavelengths in the fiber are doing.
On the other hand, metallic links that can span long distances and are reasonable to manufacture have long ago reached their theoretical limits of roughly under 500 million bits per second. They are much bulkier than fiber optic links. The metallic link is also susceptible to rust and corrosion, whereas the fiber is relatively chemically inert.
A T1 link, which is an example of a metallic link, transmits one T1 frame 8000 times per second (or one frame every 125 xcexcs). Each T1 frame contains a T1 payload with 24 Ds0 timeslots, one for each Ds0 channel with 8 bits in each timeslot. Each T1 frame also has a T1 frame bit that identifies the start of the T1 frame, so that a T1 frame has a total size of 193 bits. This results in a data stream of 1.544 Mbps (8000 frames/secxc2x7193 bits/frame).
Repeaters, which re-amplify the signal, are needed to prevent signal attenuation (loss of signal strength as a signal travels down a link) on either type of link. Metallic links attenuate the signals more than do fiber links, so more repeaters for metallic links are needed than for fiber links for a given distance. For instance, a T1 link can span a maximum of just over one mile (6000 feet) before a repeater is needed; for T3, the range is under 1400 feet. It is not unusual for fiber optic links to span 50 to 100 miles between repeaters. Fiber also costs less per foot physically than metallic links do, and the connectors at each end of a fiber link are similar in price to the connectors of a metallic link. Given the longer span between repeaters, this translates into fewer connectors, and hence lower costs, for fiber.
While metallic interfaces on port cards and repeaters are less expensive than fiber interfaces, the cost difference does not justify the reduced number of repeaters in a fiber network, nor does it justify the more expensive cabling needs even inside a switching facility. Further, the limited range of T3 metallic links has impacted the designs of several switching facilities, whereas the range of fiber links does not factor into their design.
c. Related Art
A data switch routes data packets from incoming ports to outgoing ports through a data switching matrix. There are numerous designs, of which only two will be discussed here.
One data switching matrix is a dedicated matrix that receives data packets from every incoming port card (or port interface), buffers them, and then routes them to their intended outgoing data port. Because multiple incoming packets may be destined for each outgoing data port, the links to the outgoing ports contain buffers in them that allow the data packets to accumulate until they can be delivered to the outgoing port card.
Another design uses a high-speed backplane as the delivery mechanism and circuits on each port card to examine, then accept or reject each packet. This scheme is easier to implement, but requires advanced technology to deliver high data volumes from all incoming ports to all outgoing ports. Such technologies, including low voltage differential swing (LVDS), have recently become available.
These are but a basic example of a data switching matrix designs. There are many variations on these basic concepts. These are given here as an example of how data switching can work.
Regardless of the method used, the data switching matrix can deliver a data packet from any source to any destination. Nor is the data packet limited to a single destination. Sending a data packet to multiple destinations is called multi-casting or broadcasting. Applications that might use this feature would be updates of database copies to allow local access to the database in different, distant areas, the transmission of entertainment services to multiple destinations, etc.
In order for a data switching network to route Ds0 traffic, the Ds0 channels inside the data packets must be removed and re-routed. As data switches are not designed to be synchronous Ds0 switches, a Ds0 switching matrix must be placed somewhere within the data switch to perform this function. The Ds0 switching matrix must take in data packets containing Ds0 channels, remove the Ds0 channels from the packets, switch the channels around, repackage the Ds0 channels into data packets, and place the data packets back into the data switch.
Ds0 switching nodes (Ds0 switches) contain a switching matrix that is used to route Ds0 samples from any timeslot of any incoming link to any timeslot on any outgoing link. An example of such a switching matrix is a single stage Time Slot Interchange (TSI) matrix. A TSI matrix places all incoming Ds0 samples from all incoming links into predefined locations in a randomly accessible memory (RAM). This RAM is frequently referred to as the data RAM. Many designs also place in parallel with the Ds0 channel internal status concerning the Ds0 channel in the same location in the data RAM.
A second RAM, called a control RAM, contains connection information and is used to provide a lookup address into the data RAM. Each location in the control RAM represents what an outgoing timeslot on a particular outgoing link will carry. Each location in the control RAM will address a location in the data RAM, and thus connect a particular incoming timeslot of an incoming link with an outgoing timeslot of an outgoing link. The control RAM may also possess additional control bits associated with the outgoing timeslot.
The contents of the control RAM are read out in a predetermined pattern. By following this pattern, internal timing designs within the node will assure that the intended incoming timeslot represented in the data RAM is presented to the intended outgoing timeslot.
The most efficient design for a TSI switching matrix is achieved when all Ds0 channels can be physically stored in a single RAM. If the number of Ds0 channels exceeds the limits of a single RAM, then the amount of RAM needed is the square of the number of RAM needed to store all the Ds0 channels once. This is because the job of selecting outgoing channels has to be split up among two or more identical circuits. Each outgoing circuit needs its own dedicated copy of each incoming channel in order to function without any possibility of contention occurring between it and another outgoing circuit for the same data RAM.
Today""s state of the art can write or read (access) a RAM approximately 16,384 times (16K; xe2x80x9cKxe2x80x9d denotes 1024, or 210) in a 125 xcexcs time period. If there are 32K Ds0 channels, then four memories are needed. Two RAMs are needed to store all 32K channels, splitting them among the two RAMs. This number must then double because there will be two outgoing circuits and each needs all 32K incoming channels available to it; therefore each incoming channel has to be duplicated into two sets of RAMs. If there were 48K channels there would have to be nine sets of RAMs, and if there were 68K channels there would have to be 16 sets of RAMs.
This is but a basic example of a Ds0 switching matrix design. There are many variations on this basic concept. It is given here as an example of how Ds0 switching works.
However, most data switches do not include a Ds0 switch. For this reason, the data switch will have one or more of its port interfaces removed and replaced with a Ds0 switch with a Ds0 switching matrix designed to appear as a port interface to the data switch.
Existing designs are inefficient in a number of areas. In one area, any Ds0 channel that has to be extracted from a data packet passes through the data switching matrix twice. This is because the Ds0 switching matrix is designed as an afterthought, and takes on the appearance of another port card in the data switch. Thus, the first time the Ds0 channel passes through the data switching matrix is when it is routed to the Ds0 switching matrix. The second time occurs after the Ds0 switching matrix has extracted the Ds0 channel, switched it around, and then placed it into a new data packet and returned it to the data switching matrix to be routed to the appropriate outgoing port.
Another area existing designs are inefficient in is that in order to handle large numbers of Ds0 channels to take advantage of the statistical multiplexing of a large, integrated network, a large switching matrix on the order of 256K to 1024K Ds0 channels must exist in the switch. This large matrix must take in large amounts of data packets, break out the Ds0 channels within them, route them through the matrix, make new data packets, and send them back through the switch to the destination port. As stated earlier, current Ds0 switching technology can only access a RAM 16K times in a 125 xcexcs time period. Because of the squaring problem discussed earlier, a 256K Ds0 channel matrix would take 256 data RAMs to provide for a TSI switching matrix to handle all connections.
Presently, there are two primary architectures for placing a Ds0 switch in a data switch. One concept places the Ds0 switch inside the data switch such that it does not occupy the physical space of an external port, but it consumes resources from the data switching matrix as if it were an external port card. As a result, the Ds0 switch still consumes a port interface that reduces the number of external ports the matrix can otherwise support.
A data switch cannot switch individual Ds0 channels within a data packet unless a Ds0 switch with a Ds0 switching matrix is added to the data switch. Many designs call for installing a large Ds0 switching matrix in the slot of a port card, or some other means of having the Ds0 switching matrix attach to the data switching matrix in a fashion similar to a port card. Such Ds0 switches consume resources and bandwidth within the data switch that reduces the number of port interfaces available to the data switch, increasing the costs per port of the remaining port interfaces on the data switch. A centrally located Ds0 switching matrix must be able to handle large quantities of Ds0 channels concurrently, which requires a great deal of bandwidth out of the data matrix, and a larger amount of memory than if the load is shared across each port card. The alternative to a large Ds0 switching capacity is to limit the Ds0 switching capacity of the data switch to a small fraction of the overall capacity of the data switch.
Another concept places the Ds0 switch on the port card sequentially between the incoming port and the connection to the data switching matrix to provide processing for information flows entering the data switch only. This concept solves the efficiency problems stated previously. However, this concept makes it impossible to combine Ds0 channels from different incoming ports into a single data packet. In data switches carrying a large amount of Ds0 traffic, this may lead to several problems. First, the likelihood of blocking, or the inability to find, a dedicated 64 kbps Ds0 path through the switch increases. Second, this inability to combine incoming Ds0 channels leads to the creation of many smaller data packets, which increases demand on the header processing circuitry of the network if the data packets are of variable size, or the creation of data packets with unused payload space if the packets are of a fixed size. Third, the inability to combine Ds0 channels may lead to latency, or the addition of more delay, between the source and the destination of a Ds0 channel. For instance, round trip delays starting around 140 ms, and definitely in excess of approximately 200 ms or more will affect the spontaneity of a conversation. With the inability to bundle all Ds0 channels together, more data switches must process the Ds0 channels through their Ds0 switching matrixes, increasing delay. Fourth, this design does not lend itself easily to combining channels together to maximize the use of switch and network resources, to testing, and increases delay of Ds0 traffic. Fifth, the design prevents reasonable path verification and bit error rate (BER) tests on the Ds0 switching matrix.
Notwithstanding the usefulness of the above-described voice switching matrices and port cards, a need still exists for placement of a Ds0 switch with a Ds0 switching matrix on a port card so that a node in a communications network will more efficiently handle voice communication. Furthermore, a Ds0 switching matrix is needed that is capable of reducing the processing load on a data switching matrix and attached port cards.
The present invention is directed to improving the efficiency of voice communication over a data communication network and thus gain additional efficiencies and economies of scale by providing one communications network instead of two separate communication networks for voice and data, respectively. Thus data packets may include voice channels, data, or any type of service. The invention while addressing the problems of the prior art obtains advantages that were not achievable with the prior art.
In accordance with one aspect of the invention, a Ds0 switch with a Ds0 switching matrix on each port card is connected to a data switch through in part a high speed bus thus providing switching for incoming and outgoing data packets.
In accordance with another aspect of the invention, the data switch and attached port cards are capable of switching large numbers of Ds0 channels without incurring the costs of providing for an xe2x80x9cN squaredxe2x80x9d data RAM. When the Ds0 capacity of the switch exceeds the ability of a single data RAM to hold all Ds0 channels to be switched, only additional RAMs in proportion to the number of Ds0 channels are added, not in proportion to the square of the number of Ds0 channels.
In accordance with another aspect of the invention, a communications network includes: links, at least two nodes connected to said links, each of said nodes includes a data switch having a data switching matrix, a data bus connected to said data switch, and at least one port card connected to said data bus, said port card includes a high speed data bus, and a Ds0 switch connected to said high speed data bus, said Ds0 switch includes a Ds0 switching matrix; and wherein said Ds0 switching matrix disassembles and reassembles packets after receipt of the packet by the port card from at least one of another data switch and said data switching matrix connected to said data bus.
In accordance with another aspect of the invention, a communications network node comprising: a data switch, said data switch includes a data switching matrix, a data bus connected to said data switch, and at least two port cards connected to said data bus, each of said at least two port cards includes a high speed data bus, and a Ds0 switch connected to said high speed data bus, said Ds0 switch includes a Ds0 switching matrix; and wherein said Ds0 switching matrix disassembles and reassembles packets with Ds0 channels after receipt of the packet by the port card from at least one of a source other than said data switch and from said data switching matrix connected to said data bus based on the packet.
In accordance with another aspect of the invention, a port card comprising: a high speed data bus, an intake system connected to said high speed data bus, an outgoing system connected to said high speed data bus, a port control system connected to said high speed data bus, a switch interface connected to said high speed data bus, and a Ds0 switch connected to said high speed data bus; and wherein said Ds0 switch disassembles and reassembles packets after initial receipt of the packet by at least one of said intake system and said switch interface based on the packet.
In accordance with another aspect of the invention, a port card comprising: means for receiving packets as at least one of a asynchronous transmission and a synchronous transmission, means for transmitting packets as at least one of a asynchronous transmission and a synchronous transmission, means for interfacing with a data switch, means for processing packets having Ds0 channels, and means for routing information between said receiving means, said transmitting means, said interfacing means, and said processing means; and wherein said routing means routes packets having Ds0 channels at least in part based on the respective packet to said processing means after receiving the respective packet from at least one of said receiving means and said interfacing means.
In accordance with another aspect of the invention, a telecommunications network switching method comprising: receiving a signal at a communications node, separating the signal into packets, routing individual packets with Ds0 channels to a first Ds0 switch and switching the Ds0 channels into new packets headed to the same outgoing port of the communications node when the packet includes at least one Ds0 channel destined for another communications node, routing packets based on their destination to the appropriate transmission port, manipulating Ds0 channels of packets in a second Ds0 switch into at least one of larger packets, packets with more channels for fixed size packets, and packets destined for the same outgoing port at the next communications node, and transmitting the packets as a signal to the next communications node.
In accordance with another embodiment of the invention, a method for operating a port card comprising: receiving packets from a communications conduit, routing each packet based on destination of that packet such that when the packet includes at least two Ds0 channels destined for at least two different transmission ports, the packet is routed through a Ds0 switch, when the packet includes only data, the packet is routed to a data switch, and when all Ds0 channels in the packet are directed to the same downstream communications node, the packet is routed to a data switch, interfacing with a data switch, routing each packet received from the data switch to the Ds0 switch when the packet includes at least one of at least two Ds0 channels destined for different outgoing ports and the packet contains insufficient Ds0 channels, and transmitting the packet into a communications conduit.
In accordance with an alternative embodiment of the invention, testing features are significantly enhanced and allow every data path to be easily accessible for verification. The design allows for an easy to implement method of performing BER testing of the Ds0 switching matrix and other components on the port card. Testing can be conducted concurrently while carrying live traffic.
An objective of the invention is to provide for testing capabilities of the voice switching matrix while processing and transmitting real-time communications.
A further objective of the invention is to reduce the number of networks connected to customers and managed by communications service providers.
A further objective of the invention is to have each Ds0 channel pass through the data switching matrix only once.
An advantage of the invention in transmitting data over telecommunications links is that any type of service can be placed in the data packets including Ds0 channels.
Another advantage of the invention is a reduction and/or elimination in use of the data switching matrix resources and bandwidth by the Ds0 switching matrix while providing for a flexible and inexpensive Ds0 switching architecture.
Another advantage of the invention is that flexible, robust, and thorough built in self test features may be incorporated into the port card in an alternative embodiment.
A further advantage of the invention is that Ds0 channels are not duplicated and will not need to be rejected at those port cards that do not need them, because each port card re-arranges Ds0 channels such that the data packets presented to the data switching matrix will only go to a single destination.
A further advantage of the invention is that the communications service provider reduces the operational cost of managing communications networks and thus of providing communication services to customers.